The great majority of the Internet currently utilizes Internet Protocol Version 4 (IPv4). The address space in IPv4 is becoming exhausted. The eventual exhaustion of the IPv4 address space was recognized some time ago and a common technique of dealing with it was developed. This technique employs network address translation (NAT) wherein a number of private IPv4 addresses, such as within a home or small business network, “hide” behind a single public IPv4 address.
Currently, residences and small businesses obtain access to the Internet via a number of techniques. One example is by subscribing through a cable multiple system operator (MSO); such an MSO may provide a variety of services such as broadcast television, Video-On-Demand (VOD), broadband data services, IP telephony, and the like.
In this regard, with the advent of digital communications technology, many TV program streams are transmitted in digital formats. For example, Digital Satellite System (DSS). Digital Broadcast Services (DBS), and Advanced Television Standards Committee (ATSC) program streams are digitally formatted pursuant to the well-known Moving Pictures Experts Group 2 (MPEG-2) standard. The MPEG-2 standard specifies, among other things, the methodologies for video and audio data compression allowing for multiple programs, with different video and audio feeds, to be multiplexed in a transport stream traversing a single transmission channel. A digital TV receiver may be used to decode an MPEG-2 encoded transport stream, and extract the desired program therefrom.
The compressed video and audio data are typically carried by continuous elementary streams, respectively, which are broken into access units or packets, resulting in packetized elementary streams (PESs). These packets are identified by headers that contain time stamps for synchronizing, and are used to form MPEG-2 transport streams. For digital broadcasting, multiple programs and their associated PESs are multiplexed into a single transport stream. A transport stream has PES packets further subdivided into short fixed-size data packets, in which multiple programs encoded with different clocks can be carried. A transport stream not only includes a multiplex of audio and video PESs, but also other data such as MPEG-2 program specific information (sometimes referred to as metadata) describing the transport stream. The MPEG-2 metadata may include a program associated table (PAT) that lists every program in the transport stream. Each entry in the PAT points to an individual program map table (PMT) that lists the elementary streams making up each program. Some programs are open, but some programs may be subject to conditional access (encryption), and this information (i.e., whether open or subject to conditional access) is also carried in the MPEG-2 transport stream, typically as metadata.
The aforementioned fixed-size data packets in a transport stream each carry a packet identifier (PID) code. Packets in the same elementary streams all have the same PID, so that a decoder can select the elementary stream(s) it needs and reject the remainder. Packet-continuity counters may be implemented to ensure that every packet that is needed to decode a stream is received.